224? Zoological Society. 



accompanied by specimens of Magilus antiquus, Rupp., including 

 both the shell and the animal, and of the shell and animal of a new 

 genus of Pectinibranchiated Gasteropodous Mollusca. The latter was 

 accompanied by a description by Dr. Riippell, who characterizes it, 

 as follows, under the designation of Leptoconchus . 



Testa tenuis, pellucida, subglobosa, spird depress^, subobsoletd: 

 aperturd magna, subovali, extremitatibus in contrarium versis, mar- 

 ginibus baud coalitis, dextro tenui antic^ subexpanso : columelld 

 nulls,, umbilico nullo, antice truncata, contorta. 



Afiimal proboscide elongato, retractili : tentaculis duobus, com- 

 planatis, trigonis, interne ad basin coalitis, extern^ in medio oculos 

 gerentibus : pede mediocri, operculo nullo : pallio ad marginem cir- 

 culari, hand appendiculato, ad latus sinistrum subproducto : fora- 

 mine branchiali submagno. 



The colour of the shell which constitutes the type of this new 

 genus is constantly a slightly sordid milk-white. It is sulcated ex- 

 ternally by numerous longitudinal undulated closely set lines, the 

 outer whorls encroaching on the spire of the earlier ones so as almost 

 to obliterate it. 



Length of the adult shell, 14^ lines; greatest breadth, 12-J-; 

 length of the young shell, 74-; breadth, 6. 



Individuals of all ages have the shell thin and fragile, and con- 

 stantly occur imbedded in the calcareous mass of polypes, having a 

 communication with' the sea by only a moderate opening. They 

 are found in the Red Sea, and are most frequently met with in 

 Meandrina Phrygia. 



To distinguish the shell of Leptoconchus from that of Magilus it is 

 sufficient to observe that in the latter the two margins of the aper- 

 ture are always united, while in the former genus they are always 

 disunited. The animals are distinguished by the possession and 

 the want of an operculum, and by the difference in the proboscis ; 

 the siphon of Magilus, moreover, does not occur in Leptoconchus. 



Dr. Riippell suggests that the systematic place which should be 

 assigned to this genus is near the lanthince. The number of the 

 tentacula, the oral proboscis, the mantle destitute of siphon, the pec- 

 tinated branchiae composed of closely heaped pyramids, and the ab- 

 sence of operculum, are so many marks of affinity ; to which may 

 be added some of the characters of the shell : but he states himself 

 to be perfectly aware that the difference between the habitations of 

 these genera is so wide as to afford no confirmation of the correct- 

 ness of this approximation. 



A letter was read, addressed to the Secretary by B. H. Hodgson, 

 Esq., Corr. Memb. Z.S., and dated Nepal, March 4, 1834. 



It commences by remarking on the difficulty experienced by Zo- 

 ologists in the determination of distinctive marks adequate for the 

 separation of the genera Antilope, Capra, and Ovis; and then 

 refers to the instances in which the writer has shown that the cha- 

 racter of Antilope founded on the presumed absence of cavities in 

 the cores of the horns connected with the frontal sinuses is incorrect. 

 The value of the characters which are generally admitted by authors 

 as distinguishing between the genera Capra and Ovis may, he con- 



